Thermal and abrasion resistant sintered alloy

ABSTRACT

AN ALLOY PREPARED BY MOLDING A POWDERY COMPOSITION COMPRISING 0.6 TO 2% OF CARBON, 1 TO 3% OF NICKEL, 10 TO 15% OF CHROMIUM, 0.3 TO 1.5% OF MOLYBDENUM, 5 TO 15% OF COBALT AND 1 TO 7% OF TUNGSTEN, BY WEIGHT, AND THE BALANCE BEING IRON, AND THEN SINTERING THE MOLDED COMPOSITION HAS LARGE THERMAL RESISTANCE AND ABRASION RESISTANCE.

Aug 6, 1974 KENTARO TAKAHASHI ETAL 3,827,863

' THERMAL AND ABRASION RESISTANT SINTERED ALLOY Filed Sent. 5. 1972 FIG.

0 EXAMPLE OF THIS INVENTION CONVENTIONAL SINTERED FERRO-ALLOY HARCNFLSSNORMAL IOIO 2OO 300 4OO sOO sOO (c) TEMP TRANSFORMATION TEMP.

E 0 EXAMPLE OF THIS INVENTION 5 CONVENTlONAL SINTERED g O25 FERRO-ALLOYa x CONVENTIONAL cAsT ALLOY 12 02 ll: 0 [I] LL O.l5 x O -o E 0.! D O E0.05

L v AL IOO 2OO 3OO 4 00 50 0 (c) TRANSFORMATION TEMP.

rates 3,827,863 THERMAL AND ABRASION RESISTANT SINTERED ALLOY KentaroTakahashi, Ohmiya, Minoru Hasegawa, Saitama, and Kaoru Nara, Kawaguchi,Japan, assignors to Nippon Piston Ring Co., Ltd., Tokyo, Japan FiledSept. 5, 1972, Ser. No. 286,393 Claims priority, application Japan,Sept. 2, 1971, 46/ 66,981 Int. Cl. B22f 1/00 US. Cl. 29182 1 ClaimABSTRACT OF THE DISCLOSURE An alloy prepared by molding a powderycomposition comprising 0.6 to 2% of carbon, 1 to 3% of nickel, 10 to 15%of chromium, 0.3 to 1.5% of molybdenum, 5 to 15 of cobalt and 3 to 7% oftungsten, by weight, and the balance being iron, and then sintering themolded composition has large thermal resistance and abrasion resistance.

BACKGROUND OF THE INVENTION A publicly known metal such as chromium,cobalt, tungsten, etc. has not only a large abrasion resistance but alsois prominent in its characteristics at elevated temperatures and isapplied in various fields. However, such a metal has many problems to besolved when it is used as sintered parts for a machine. That is, such ametal has a high melting point so that the sintering temperature is, ofnecessity, required to be elevated and the sintering time has to beextended, and, therefore, it is naturally disadvantageous in cost.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is agraph showing the hardness at elevated temperatures of sintered alloysof Examples 1 and 2 and on a conventionally cast iron and a sinterediron alloy.

FIG. 2 is a graph showing the abrasion resistance of sintered alloys ofExamples 1 and 2 and of a conventionally cast iron and a sintered ironalloy.

DETAILED DESCRIPTION OF THE INVENTION The sintered alloy of the presentinvention is obtained by adding 15 to 25% of special alloy powderconsisting of, by weight, 1 to 3% of carbon, 55 to 65% of chrmium, 25 to30% of tungsten and to 20% of cobalt to a powdery composition mainlycomposed of iron and containing carbon, nickel and molybdenum, andcompression-molded the resulting powdery composition mainly composed ofiron and comprising, by weight, 0.6 to 2% of carbon, 1 to 3% of nickel,0.3 to 1.5% of molybdenum, to of chromium, 5 to 15% of cobalt and 3 to7% of tungsten under a pressure of 3 to 6 ton/ cm. and sintering it inan atmosphere at 1120 to 1170 C. for 30 to 60 minutes.

3,827,863 Patented Aug. 6, 1974 When the carbon content is less than0.6% by weight, the alloy changes to a ferrite-excessive structure sothat high hardness cannot be expected while, with more than 2%, thealloy changes to a cementite-excessive structure which is high inbrittleness.

Nickel strengthens the base structure of the alloy and improves thethermal resistance and abrasion resistance. However, the effect is smallwith a nickel content of less than 1%, while, when it is more than 3%,the base structure locally turns to martensite so that the hardnessincreases unnecessarily and the structure and the hardness loseuniformity.

Molybdenum increases the tenacity of alloy as well as the impactstrength and endurance limit, and, on the other hand, improves the heattreatment property and stabilizes the structure after sintering andfurther possesses a synergistic effect, with other elements. However,there is no elfect with less than 0.3% of molybdenum and even with morethan 1.5% no increase in eifect corresponding to the increase is notobtained.

In connection with the manufacturing of the alloy powder and structureand characteristic of sintered material, 15 to 25 of alloy powder areselected and chromium, cobalt and tungsten are established at 10 to 15%,5 to 15% and 3 to 7%, respectively.

In the sintered alloy of the present invention, from a viewpoint ofproviding the material with a high density and improving the lubricatingproperty, it is very advantageous to impregnate molten lead into thealloy after the alloy is molded and sintered. In this case, the amountof lead impregnated has been experimentally confirmed to be preferablywithin the range of 0.05 to 5% by weight. That is, with less than 0.05%the effect of impregnation is not remarkable and the impregnation ofmore than 5% of lead involves a problem in strength from the relationwith the density of material before impregnation.

The present invention will be further illustrated by the followingExamples by which the present invention is not intended to be limited.All percents are by weight.

EXAMPLE 1 18% of a special alloy powder (150 mesh) comprising 0.74% ofgraphite powder (325 mesh), 1.08% of carbonyl nickel powder (250 mesh),0.35% (as molybdenum) of ferro-molybdenum powder (150 mesh), 55 to 65%of chromium, 25 to 30% of tungsten and 5 to 20% of cobalt were added toreduced iron powder mesh) as iron powder (at this time, the actualchromium content was 10.8%, tungsten 5.4% and cobalt 1.8% Then, cobaltpowder mesh) was added thereto so that the cobalt content became 5.5%and further 1% of zinc stearate was added and mixed as a lubricant. Themixture was molded under a pressure of 4 ton/cm. and sintered at 1120 to1170 C. in an atmosphere of decomposed ammonium gas. This sinteredmaterial had a density of 6.5 g./cm. and a hardness on the Rockwell Bscale of 94'.

EXAMPLE 2 A sample was prepared by adding 2.3% of the special alloypowder under the same conditions as described in Example 1 and then thesample was impregnated with molten lead. The final composition of thesample was 1.71% of carbon, 2.83% of nickel, 1.33% of molybdenum, 14.1%of chromium, 7.0% of tungsten and 14.2% of cobalt and the lead contentafter lead impregnation was 3.8%. The sintered material had a density of6.7 g./cm. and a hardness on the Rockwell B scale of 96.

FIGS. 1 and 2 show the results of measuring the hardness at elevatedtemperatures and abrasion using a valve sheet abrasion testing machine(number of rotation 3000 rpm, spring pressure 35 kg, valve velocity atthe time of valve closing 0.5 rn./sec., width of valve 1 mm., testrepeating 3 number 8x10 material SUI-1 31 B) on the sintered alloy ofExamples 1 and 2 in comparison with a conventionally known cast iron andsintered ferro alloy. As is apparent from the results obtained thesintered alloy of the present invention was higher in hardness atelevated temperatures in comparison with the conventionally known castiron and sintered ferro iron, and was excellent in hardnesscharacteristics. In the abrasion test the conventionally known cast ironand sintered ferro alloy had peaks at 300 C. and 400 C., respectively,and the sintered alloy of the present invention was lower in abrasionand very stable at elevated temperatures. The compositions of theconventionally known cast iron and sintered ferro alloy were as follows:

Sintered ferro alloy:

Carbon 1%, copper 3%, chromium 3%, and balance 11'011. Cast iron:

Carbon 3.02%, silicon 2.11%, manganese 0.48%, chromium 0.81%.

The sintered alloy of the present invention is advantageous in cost, andexcellent in thermal and abrasion resistance with improved sinteringtime -by alloying chromi- References Cited UNITED STATES PATENTS3,471,343 10/1969 Koehler -125 3,495,957 2/1970 Matoba et al 29182.l2,662,010 12/1953 Ahles 75123 J 2,562,543 7/1951 Gippert 75123 KBENJAMIN R. PADGETT, Primary Examiner B. HUNT, Assistant Examiner US.Cl. X.R.

29-1871, 156.7 A; 75128 B, 128 D, 128 W

